The present invention pertains to a hardenable fluorinated copolymer of vinylidene fluoride (C.sub.2 H.sub.2 F.sub.2) and tetrafluoroethylene (C.sub.2 F.sub.4), a hydroxylated allyl ether and a vinyl ether. This copolymer, which is soluble in organic solvents, is particularly recommended for the manufacture of protective coatings, i.e. paints and varnishes.
The fluorinated polymers are known for their good mechanical properties and their excellent resistance to chemical products and weather. However, their lack of solubility in conventional solvents makes them unusable for certain applications such as, for example, resin for paints and varnishes where their properties are sought for the manufacture of coatings with good resistance and easy maintenance.
In order to benefit from these properties of the fluorinated polymers while avoiding their drawbacks, means have been sought to make them soluble in the conventional organic solvents. In order to accomplish this, it is known to decrease the crystallinity of fluorinated polymers by copolymerization of ethylenically unsaturated monomers at least one of which is fluorinated.
In addition, to use such copolymers it is desirable for certain applications, particularly for their use in the manufacture of paints and varnishes, to preserve for them a sufficient degree of rigidity and to make them hardenable by incorporating functional groups into their structure.
Such cross-linkable fluorinated copolymers are described in French patent 2,597,873 and 2,569,703. These products are obtained by copolymerization of chlorotrifluoroethylene, fatty acid ester and hydroxylated or ethoxylated allylglycidyl ether. These copolymers may possibly contain less than 20% of another nonfluorinated comonomer. If these copolymers contain more than 20% of the previously mentioned comonomer, they lose their solubility in the solvents as well as their transparency. In addition, the introduction of the fluorine by the use of C.sub.2 F.sub.3 Cl alone, also brings along the chlorine atom which is not desirable in large amounts with regard to optical properties and resistance to corrosion.
In Japanese publication 59-174,657/84, there is also described a hardenable, cross-linkable copolymer based on vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, a vinyl ester and a hydroxylation agent. This copolymer, which contains 5 to 80% of chlorotrifluoroethylene groups and is based on vinyl ester, has the drawback that after hydrolysis it provides a very strongly colored copolymer solution which damages the transparency of the varnishes subsequently created from this product.